1. Field of the Invention
This invention relates generally to a system and concomitant methodology for handling incoming calls to and outgoing calls from a mobile user; this invention relates, more particularly, to CACH-EKTS procedures and circuitry used with a central office and an associated base station to effect such handling.
2. Description of the Prior Art
A typical mobile system is composed of numerous mobile units, such as handsets operated by individual system users, which home-on an associated base station. Typically each base station serves a number of mobile units that lie within a simply connected geographical area--a cell--identified to that single base unit. Most of the current cellular mobile systems use a registration method to keep track of the locations of the mobile units. A specific base station serves as a controller for the units within an assigned cell. Each mobile unit is required to inform, that is, register with, the base station its location when the user moves from the original cell into a new cell. This registration process is typically accomplished automatically by the mobile unit, but the registration may also be effected manually by the user of the unit. The base station will, in turn, pass the registration information to the serving switching office. Since a conventional cellular mobile system generally covers a geographical area larger than a single switching office, the registration process requires the coordination among a plurality of switching offices, and such registration process may involve the use of centralized databases in the serving network to keep track of mobile unit locations.
Representative of the prior art in this area of technology is the digital mobile network configuration of the EWSD switching system supplied by the Siemens AG. In this EWSD configuration, a base station serving a cell is connected via a digital carrier, such as DS1, to a radio network controller which functions to off-load processing of the radio part of the call from the switching office. The radio network controller is further connected, also via digital carrier links, to conventional line/trunk groups interfacing a switch in the switching center which ultimately switches the call. A network management module for the radio subsystem, that is, base station and radio network controller, is coupled to the switches via an interposed processor which coordinates management activities. The mechanism provided by such an architecture is based on a centralized database which contains the mobile subscribers home information. The switches themselves have only temporary information about visiting subscribers at any particular instance. Using transaction capabilities over a common signaling network such as SS7, the information from the centralized databases is transferred to the switches when necessary to handle, for example, handoffs.
There are applications of mobile systems in which the use of multiple switching offices is not a strict requirement. The service area of a single switching office is, in these applications, sufficient for many practical situations such as wireless CENTREX. The type of switching office can then be a central office (CO) belonging to the public switching network.
In these limited service area applications, the use of centralized databases, the process of registration between the handset, base station and the switching network, and the use of complicated and dedicated signaling and switching procedures may be too expensive when compared to a method that would be limited to a single switching office and which would only use existing generic signaling and switching procedures.
Also, ISDN technology is now being deployed in the telephony field and ISDN is becoming the accepted method for evolving voice and data communications. ISDN uses a well-defined and standardized signaling protocol between a user terminal and the serving switching office to allow call set-up, connection, and termination procedures as well as offering supplementary services. The definition of the ISDN technology is included in the ANSI standards and CCITT recommendations.
One supplementary service offering built upon the principles of ISDN is the Electronic Key Telephone Service (EKTS); EKTS allow multiple telephone sets to simultaneously respond to an incoming call for a given telephone number, for instance, an appearance of a directory number (DN) on multiple terminals. EKTS also allows these telephone sets to make outgoing calls from the DNs, or to bridge onto an existing call for an active DN. An ISDN-based EKTS system uses enhancements to the basic ISDN technology to offer EKTS capability. In addition, the Call Appearance Call Handling (CACH) feature of EKTS allows multiple call appearances of the same DN on multiple terminals as well as on a single terminal.
Thus, a need exists in the art for mobile services which utilize existing features and functions offered by a single switching office having ISDN capability, including CACH- EKTS, thereby eliminating the need for special procedures and databases to handle such services.